netdev - [PATCH net] net: usbnet: fix softirq storm on suspend

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Date:	Mon,  3 Sep 2012 10:26:18 +0200
From:	Bjørn Mork <bjorn@...k.no>
To:	netdev@...r.kernel.org
Cc:	linux-usb@...r.kernel.org,
	Bjørn Mork <bjorn@...k.no>,
	Ming Lei <ming.lei@...onical.com>,
	Oliver Neukum <oneukum@...e.de>
Subject: [PATCH net] net: usbnet: fix softirq storm on suspend

Suspending an open usbnet device results in constant
rescheduling of usbnet_bh.

commit 65841fd5 "usbnet: handle remote wakeup asap"
refactored the usbnet_bh code to allow sharing the
urb allocate and submit code with usbnet_resume. In
this process, a test for, and immediate return on,
ENOLINK from rx_submit was unintentionally dropped.

The rx queue will not grow if rx_submit fails,
making usbnet_bh reschedule itself.  This results
in a softirq storm if the error is persistent.
rx_submit translates the usb_submit_urb error
EHOSTUNREACH into ENOLINK, so this is an expected
and persistent error for a suspended device. The
old code tested for this condition and avoided
rescheduling.  Putting this test back.

Cc: <stable@...r.kernel.org> # v3.5
Cc: Ming Lei <ming.lei@...onical.com>
Cc: Oliver Neukum <oneukum@...e.de>
Signed-off-by: Bjørn Mork <bjorn@...k.no>
---
Sorry for not noticing this before, but commit 65841fd5
makes usbnet autosuspend completely unusable.  The device
is suspended fine, but burning one CPU core at full load
uses a tiny bit more power making the power saving 
negative...

I hope this can go into 3.6 and 3.5-stable ASAP. It is
a hard to notice regression, but all the same a serious
one.


Thanks,
Bjørn


 drivers/net/usb/usbnet.c |   16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/net/usb/usbnet.c b/drivers/net/usb/usbnet.c
index fd4b26d..fc9f578 100644
--- a/drivers/net/usb/usbnet.c
+++ b/drivers/net/usb/usbnet.c
@@ -1201,19 +1201,26 @@ deferred:
 }
 EXPORT_SYMBOL_GPL(usbnet_start_xmit);
 
-static void rx_alloc_submit(struct usbnet *dev, gfp_t flags)
+static int rx_alloc_submit(struct usbnet *dev, gfp_t flags)
 {
 	struct urb	*urb;
 	int		i;
+	int		ret = 0;
 
 	/* don't refill the queue all at once */
 	for (i = 0; i < 10 && dev->rxq.qlen < RX_QLEN(dev); i++) {
 		urb = usb_alloc_urb(0, flags);
 		if (urb != NULL) {
-			if (rx_submit(dev, urb, flags) == -ENOLINK)
-				return;
+			ret = rx_submit(dev, urb, flags);
+			if (ret)
+				goto err;
+		} else {
+			ret = -ENOMEM;
+			goto err;
 		}
 	}
+err:
+	return ret;
 }
 
 /*-------------------------------------------------------------------------*/
@@ -1257,7 +1264,8 @@ static void usbnet_bh (unsigned long param)
 		int	temp = dev->rxq.qlen;
 
 		if (temp < RX_QLEN(dev)) {
-			rx_alloc_submit(dev, GFP_ATOMIC);
+			if (rx_alloc_submit(dev, GFP_ATOMIC) == -ENOLINK)
+				return;
 			if (temp != dev->rxq.qlen)
 				netif_dbg(dev, link, dev->net,
 					  "rxqlen %d --> %d\n",
-- 
1.7.10.4

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